Sub-half micron multilevel metallization is one of the key technologies for the next generation of very large scale integration ("VLSI"). The multilevel interconnects that lie at the heart of this technology require planarization of high aspect ratio features such as plugs and other interconnects. Reliable formation of these interconnects is very important to the success of VLSI and to the continued effort to increase circuit density and quality on individual substrates and die.
Conventional chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques are used to deposit electrically conductive material into the contact holes, vias, trenches, or other patterns formed on the substrate. One problem with conventional processes arises because the contact holes or other patterns often comprise high aspect ratios, i.e., the ratio of the height of the holes to their width or diameter is greater than 1. The aspect ratio of the holes increases as advances in technology yield more closely spaced features.
Referring to FIG. 1, a substrate 10 including a hole 11 formed within an electrically insulative or dielectric layer 12 thereon, such as for example, a silicon dioxide or silicon nitride layer is shown. It is difficult to deposit a uniform metal-containing layer into the high aspect ratio hole 11 because the metal-containing layer often deposits on the sidewalls 14 of the holes and across the width of the hole to eventually converge across the width of the hole before it is completely filled, thus forming voids and discontinuities within the metal-containing material. Thereafter, the high mobility of metal atoms surrounding the voids causes the atoms to diffuse and minimize the surface area of the voids forming circular shaped voids as shown in FIG. 1. These voids and discontinuities result in poor and unreliable electrical contacts.
One method used to reduce the likelihood that voids will form in the contact holes, vias, trenches, or other patterns, is to "planarize" the metal at high temperatures. Formation of a continuous wetting layer on the substrate is the key for successful planarization at high temperatures. It has been previously discovered that a thin conformal aluminum film is a good wetting layer for subsequent physical vapor deposition and planarization techniques performed at high temperature (.gtoreq.350.degree.). One method is the use of a wetting layer deposited using chemical vapor deposition (CVD) techniques, i.e., an aluminum layer, as the planarization wetting layer. Successful CVD Al or Cu deposition has been achieved by initially depositing conformal Ti and TiN layers which function as both a barrier layer and a nucleation layer for improving the CVD layer. Recent experiments show that the Ti and TiN layers do not have to be conformal to improve the deposition and performance of the CVD Al or Cu layer. Similarly, Ta and TaN layers have functioned well as barrier layers and nucleation layers for copper deposition. Successful wetting layers of Ni, NiV, and V have also been used to fill patterns during manufacture of magnetic heads.
Oxidation of metal layers, such as Ti, TiN, Ta, TaN, Ni, NiV, and V, is known to hinder use of the layers for nucleation of subsequent metal layers and can increase the electrical resistance of the combined layers. Thus, successful metallization sequences have typically involved deposition of the wetting layer and subsequent metal layers, e.g., Ti or TiN and aluminum, or Ta or TaN and copper, without exposure to oxygen. The sequential deposition steps can be performed in the absence of oxygen by combining the various deposition chambers on an integrated platform such as the Endura.TM. processing system which is available from Applied Materials, Inc., of Santa Clara, Calif. However, the various chambers required to perform the deposition sequences operate for significantly different time periods and many of the chambers are underutilized. Arrangement of the various chambers on different integrated platforms would improve productivity except for detrimental exposure to oxygen. Furthermore, oxygen plasma treatment of metal layers, e.g., O.sub.2 plasma stuffing of Ti or TiN, and ex situ processes such as furnace annealing and rapid thermal processing (RTP) have known benefits on metal layers, such as enhanced barrier properties, but adversely affect subsequent metal layers, such as by causing deterioration in crystal orientation, grain growth, fill properties, and reflectivity.
Deposition of a thin layer of non-oxidized metal on an oxidized metal layer has been proposed to improve nucleation of the CVD aluminum layer, but requires additional process time and additional deposition chambers. Nucleation of aluminum or copper may be improved if the underlying metal layers, e.g., Ti, TiN, Ta, TaN, Ni, NiV, and V layers, did not contain oxygen near the surface. Thus, there is a need for removing or reducing oxidation of metal layers prior to deposition of a metal layer to fill high aspect ratio contact holes, vias, trenches, and other patterns.